Light-emitting diodes (LEDs) are used in numerous products for backlighting, general illumination, and other purposes. Without modification, LEDs typically emit light having a narrow range of wavelengths that can be undesirable for many applications. Lighting devices including LEDs, therefore, often include optical components to modify or supplement light from the LEDs. These optical components can include color-converting materials, such as composites including phosphor or other color-converting particles that absorb light at certain wavelengths and emit light at different wavelengths. For example, some lighting devices include LEDs that emit blue light and color-converting particles that absorb some of the blue light and convert it into yellow light. The combination of blue light from the LEDs and yellow light from the color-converting particles can appear white. Known color-converting particles useful for this purpose include yttrium aluminum garnet doped with suitable rare earth elements, such as cerium.
FIG. 1 is a partially-schematic cross-sectional view of a conventional lighting device 100 including a heat sink 102 having a trench 104 and an LED 106 within the trench 104. The device 100 further includes an optical component 108 extending over the trench 104 and a fill material 110 within the trench 104 around the LED 106. The optical component 108 includes color-converting particles (not shown) suspended within a transparent matrix material. The color-converting particles absorb and convert a portion of the emitted light from the LED 106. Another portion of the emitted light either passes through the optical component 108 without being converted or is reflected back into the trench 104. The amount of converted light relative to unconverted light causes the device 100 to have a characteristic color, which can be quantified, for example, as correlated color temperature (CCT) or as a set of coordinates on a chromaticity diagram. For many applications, it is desirable to have multiple lighting devices with similar colors. For example, lighting products incorporating multiple lighting devices with similar colors generally are more aesthetically appealing during use than lighting products incorporating multiple lighting devices with widely varying colors. Furthermore, manufacturers of lighting products often specify lighting characteristics for particular product designations. Incorporating lighting devices with similar colors into all lighting products having the same product designation can be useful to match specified characteristics, to satisfy customer expectations, and/or to meet industry standards.
Variables affecting the amount of converted light relative to unconverted light for a lighting device can include the sizes and concentration of color-converting particles within a color-converting material as well as the thickness of the color-converting material. The sizes of the color-converting particles are often well controlled using mesh screening and/or other conventional techniques. Similarly, selecting a suitable matrix material, uniformly distributing the color-converting particles throughout the matrix material, and other conventional techniques can be sufficient to cause the concentration of the color-converting particles to be relatively consistent. The thickness of the color-converting material, however, can be difficult to control adequately using conventional techniques and can be highly susceptible to process excursions. As a result, optical components of lighting devices from the same manufacturing processes often have significantly different thicknesses, causing the lighting devices to have significantly different color outputs. Although lighting devices are generally binned according to color after manufacturing to yield separate batches having similar colors, this only partially addresses the issue of color variability. For example, even if binning is used, wide color variation among lighting devices can cause large numbers of the lighting devices to fall into undesirable bins having relatively low market values. Furthermore, testing and binning are additional processing steps that increase manufacturing costs.
For one or more of the reasons stated above, and/or for other reasons not stated herein, there is a need for innovation in the field of lighting devices directed to enhancing the accuracy and/or precision of color control in manufacturing processes for the lighting devices.